B: Carbohydrates

Question 1

Similarities between starch & glycogen structure

Answer 1

• Homopolymers of alpha-D glucose
• Both have 1,4 glycosidic bonds with 1,6 linked branched
• Both are digested by alpha-amylase which breaks down 1,4 glycosidic bonds

Question 2

Differences between starch & glycogen structure

Answer 2

• Amylopectin (branched starch) has branch points recurring every 24-30 glucose residues.
• Glycogen has branch points recurring every 8-12 glucose residues –> its more compact

Question 3

Glycoconjugate?

Answer 3

Oligo + polysaccharides bond covalently to biomolecules (proteins + lipids) to make a glycoconjugate via glycosylation.

Question 4

Glycoconjugates are in important in:

Answer 4

• Cell to cell recognition
• Forming interactions between cells and extracellular matrix
• Cell migration during development
• Blood clotting
• Immune response
• Wound healing.

Question 5

Monosaccharides

Answer 5

either aldehydes or ketones with two or more hydroxyl groups

Question 6

Carbohydrate nomenclature

Answer 6

D = right L= left
If highest chiral carbon is with OH group is on the left side = L, if on the right side = D

Question 7

D-glucose

Answer 7

Most common monosaccharide in our cells
Aldohexose
Cyclic structure is energetically more stable than linear form
Has two stereoisomers (alpha and beta) –> anomers
6 membered ring structures are called pyranose
Covalent bond formed between carbonyl group (C1) and oxygen of hydroxyl group (C5)

Question 8

Disaccharide formation

Answer 8

Monosaccharides join by condensation reaction to form glycosidic bonds.

Question 9

Glycosidic bond?

Answer 9

Covalent bond between hydroxyl group of one sugar and carbonyl (anomeric) carbon of another

Question 10

Types of glycosylation

Answer 10

Sugars can be linked to proteins through:
- Hydroxyl groups: O-linked glycosylation
- Amino group - N-linked glycosylation

Question 11

What determines blood type?

Answer 11

Blood type is determined by composition of oligosaccharides attached to glycoproteins of human cells.
All humans can synthesise O antigen.

Question 12

Type A blood

Answer 12

Type A blood = Enzyme modifies O antigen with N-acetylgalactosamine (GalNAc)

Question 13

Type B blood

Answer 13

Enzyme adds galactose (Gal) to O antigen

Question 14

Lectin

Answer 14

recognise and bind with very high affinity to specific oligosaccharides.